Recent advances in IS have led to the development of electronic networks that enable thousands of geographically dispersed individuals, who are typically strangers from diverse organizational, national, and demographic backgrounds, to interact (Sproull & Faraj, 1995). In these networks, individuals engage in knowledge sharing and problem solving through message postings offering professional advice, storytelling of personal experiences, and debate on relevant issues (Wasko & Faraj, 2000). Individuals benefit from these networks since they gain access to new information and expertise related to their practice that are often not available locally. Based on previous research (Wasko & Teigland, 2004), we define an electronic network of practice (ENOP) as a self-organizing, open activity system focused on a shared practice that exists through computer-mediated communication. Despite the growing interest in online social structures such as electronic networks of practice, we know surprisingly little about how or why these structures support knowledge exchange (Desanctis & Monge, 1999; Lin, 2001). Thus, the goal of this exploratory research is to investigate electronic networks of practice by drawing upon theories of public goods and collective action. Building upon work by Fulk and colleagues (Fulk, Flanagin, Kalman, Monge, & Ryan, 1996), we investigate ENOPs as a form of collective action by examining two fundamental research questions: (1) what is the pattern of interaction underlying knowledge exchange in an ENOP and (2) why do some individuals participate more than others in an ENOP. The article concludes with a discussion and areas for future research.